1. Field of the Invention
The present invention relates to an image forming apparatus for reading image data from a source or original document, and printing the document image on recording paper (hereinafter simply called paper).
2. Description of the Related Art
Some kinds of image forming apparatuses, such as copying machines, incorporate a function, called an interrupt mode, for suspending processing currently in progress and performing another processing. Many of recent image forming apparatuses incorporate an automatic document feeder (ADF) in which multiple originals are placed and fed one by one for reading of image data. Suppose that one or more unread originals (interrupted job originals) remain in the automatic document feeder upon execution of another processing in an interrupt mode. In this case, the use of the automatic document feeder in the interrupt mode causes a mix-up between the precedent interrupted job originals and interrupt job originals. To avoid this, any conventional way of setting an interrupt mode is to prohibit users from selecting any mode with the potential to go into competition with the interrupted job.
For example, there are techniques for making the transition to the interrupt mode in such a way that allows the execution of the interrupt job only after a number of copies set for the interrupted job are completed (for example, refer to Japanese patent laid-open No. 10-026905). There is also another type of techniques for competition control and warning upon setting of an interrupt job. When setting of an interrupt mode leads to processing competition, this type of techniques provides a warning indication to urge the user to change the setting (for example, refer to Japanese patent laid-open No. 2001-010169).
Thus there is no conventional image forming apparatus that can determine, based on the results of checking the states of originals and paper in response to a request to execute an interrupt mode, which operation mode to select from those usable in the interrupt mode. In other words, since the conventional image forming apparatuses have previously eliminated operation modes with the potential to go into processing competition, operation modes executable in an interrupt mode are limited upon setting the interrupt mode. This makes the conventional image forming apparatuses less user-friendly.